1. Field of the Invention
The present invention relates to a range finding device of a triangulation system for use in an automatically focusing camera.
2. Description of the Prior Art
In conventional range finding devices for use in automatically focusing cameras, infrared light is radiated toward an object and the light reflected from the object is received by a photoelectric conversion element to thereby find the range from the camera to the object by means of a triangulation system. In these systems, generally, the infrared light is stopped down or reduced in diameter so as to increase the possible range of the device to a point as far distant as possible. Therefore, the range finding zone in a picture is so narrow that, for example, when two people standing side by side are photographed, if the center of the range finder is directed to an intermediate position between the two people, so that the background appearing behind the two people is focused, erroneous range finding occurs. In order to solve this problem, various means for widening the range finding zone in a picture have been proposed.
For example, U.S. Pat. No. 4,470,681 discloses a system in which respective focusing lenses for an infrared light emitting diode and for a light receiving element are linked with each other so as to be horizontally movable. That is, both the light emitting and light receiving lenses are moved while the same point is focused by the two lenses, so as to scan a surface of an object with infrared light. The aforementioned U.S. Pat. No. 4,470,681 further discloses a technique in which each of the focusing lenses to be used for infrared light emitting diodes and for light receiving elements are made of multiplex eyes (lens arrays) and range finding is performed on a number of points which are equal in number to the number of lens arrays.
Furthermore, Japanese Unexamined Patent Publication No. 193406/1984 discloses a device in which an object is scanned while rotating a light emitting source. A diffraction grating is disposed in front of the light emitting source so as to generate first-order diffraction beams at the opposite sides of a main beam (zero order) to thereby scan the surface of the object by using those three beams.
In the above-mentioned devices in which two focusing lenses are horizontally moved and in which a light emitting source is rotated, respectively, it is possible to perform multi-points range finding by scanning the surface of an object. However, the provision of movable parts causes problems in durability as well as reduction in accuracy.
In the system using lens arrays, there is a troublesome problem in that the axes of the respective lens arrays for the light emitting and receiving elements must coincide with each other. Further, the use of such lens arrays makes the range finding portion bulky, resulting in limitations in the design of the camera.